Generally, digital light processing (DLP) projectors include a digital micro-mirror device (DMD). The DMD is configured for superimposing spatial information on an incident light and emitting the light. Referring to FIG. 4, the DMD includes a base 10, a number of outer pads 101 are disposed on the base 10, a micro-mirror array 111 (only a number of micro-mirrors are shown), and a number of bonding wires 121. The micro-mirror array 111 is disposed on the base 10 and is electrically connected to the outer pads 10 via the bonding wires 121. The bonding wires 121 are configured for transferring control signal to the DMD to control a rotation of each micro-mirror of the micro-mirror array 111.
In manufacture of the DMD, the bonding wires 121 are bare at the base 10. When an incident light strikes the DMD, the bare surface of the bonding wires 121 on the base 10 may reflect the incident light to produce stray light and may in turn be projected onto a screen along with the desired image.
It is desired to provide a projection optical system which can overcome the above-described deficiency.